The ATS's relatively petite size and weight is instantly apparent, with eager directional changes and terrific balance—50:50 front to rear.

Having established a sports-sedan foothold with the CTS, Cadillac used it to kick teeth in with the jackbooted, supercharged CTS-V, in sedan, coupe and loony-wagon guises. But that CTS has always been a tweener, closer in size, mass and outlook to deluxe midsizes like the 5 Series.

The ATS, in contrast, stalks the 3 Series so closely that the BMW might feel Cadillac's clammy breath on its neck. The ATS rides a 1.3-in. shorter wheelbase, but length, width and height are all within 0.4 in. of the Bimmer.

The laser targeting extends to weight, where Cadillac engineers' gram-by-gram excision has paid off. The ATS's 3464-lb. curb weight is just 26 lb. heavier than that of the 328i, a win for General Motors, whose cars and trucks have often been the fat kids of their various classes.

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Compared with the CTS, the ATS's relatively petite size and weight was instantly apparent, with more eager directional changes and terrific balance—50:50 front to rear, baby—as we hung it around Ohio's best curves. The ZF electric-assist steering is accurate, if not as intimate with the road as the BMW's. And the ATS's stickier tires help eke out a bit more skidpad grip, at 0.89g versus 0.88. Brakes were another win for the ATS, with standard Brembos providing shorter stops and a more linear pedal than the 328i's binders.

While the ATS's sales prospects in China may have partially dictated a moreconservative shape, a sedan that looked a bit lifeless on auto-show floors came alive on the open road: The ATS's lines and details, including a V-shaped hood bookended by striking, vaguely Art Deco headlamps, began to grow on even staff skeptics. The charm offensive continued inside, where the ATS's contemporary, multi-hued cockpit provided an appealing (and more gender-neutral) alternative to the 3 Series's Berlin-black machismo.

The stylish vibes were short-circuited somewhat by Cue (Cadillac User Experience), a new screen-based, smartphone-style infotainment system. As with BMW's original iDrive, the firstgeneration Cue is a temper-baiting ergonomic muddle. Cue's controls—whether the multi-directional toggle widget on the steering wheel or its stubborn flushmounted capacitive controls—ignore orders like a stoned teenager working the drive-through window. Cadillac's much-hyped haptic screen feedback is felt as unpleasant knocks against your fingertips. Strong points include pleasing graphics and proximity sensors that pop additional functions onto the screen as your hand approaches. As with Ford's system, Cue can be sweet-talked via voice and it gets better with familiarity. But it still requires the steady hands of a surgeon and too much eyes-off-the-road.

Come test time, the ATS appeared to have a nominal edge, given that its turbo 4-cylinder (cribbed from the front-drive Buick Regal GS) has 32 more horsepower and five more pound-feet of torque than the BMW's four. The Tremec 6-speed manual, of note, can only be had on this 2.0-liter model, while the 6-speed automatic is the only choice with the 200-bhp 2.5-liter inline-4 or the 318-bhp 3.6-liter V-6. Only the V-6 model offers all-wheel drive.

That is, until we revved the ATS's engine, dropped the clutch and tore off down the road. The ATS was ultimately tripped up by two things that left it especially vulnerable against the BMW: its engine and gearbox.

Cadillac claims the ATS achieves peak torque at 1700 rpm (the BMW can call up full grunt as low as 1250 rpm), but you'd never know it. Launching the Caddy proved difficult, with the car either bogging or frittering power away through excessive wheelspin. And though there's power lurking in its little 4-banger, the ATS suffers from turbo lag, a congested-sounding exhaust note and a power curve that feels too compressed. All the urge seems concentrated between 2500 and 6000 rpm, where the more flexible BMW zings and sings anywhere from 1500 to 7000 rpm.

Worse, the manual gearbox recalls the Ghost of Saabs Past, clanking its awkward chains. Throws are a bit long and loose-jointed; the Camaro ZL1's manual is a paragon in comparison. Chasing the BMW on wooded back roads, I occasionally jammed the 3rd-to-2nd shift, killing forward progress.

With a tight powerband and short gearing, the Cadillac requires two shifts, three gears and 6 seconds to reach 60 mph. That puts the ATS over a halfsecond behind the BMW, which needs only one shift to pass 60 mph. Yet, when the ATS carries its ample momentum through curves, this is still a fun and confident sedan. Though we did find ourselves wondering whether another ATS, with the stronger V-6 and an automatic transmission, will end up being the enthusiast's choice, clutch pedal or not.

Cadillac has achieved one goal: qualifying the ATS as a legitimate player in international competition. But its baby needs more training and technique if it hopes to stand atop the podium with a star-spangled anthem playing behind it.